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Dams which were primarily used for irrigation and water supply in ancient days makes their presence inevitable through their important roles in other arenas such as flood control, hydropower development, navigation, sediment control and water quality etc., as well. The overall basin development depends largely on various dams constructed at various salient location. To the world population –presently at 8 billion- the demand for water which is growing at 2 to 3% annually will be a concern and dams render a helping hand in that perspective. Concrete dams plays a prominent role. The failures of concrete gravity and arch dams are rare compared to other types. Comprehensive studies on dams attributed the failure modes to overtopping, foundation problems, piping, sliding, structural failure, inadequate spillways, earthquake motions and faults in operations etc. Thermal loading is a concern when there are large variations in temperature. Earthquakes can become a cause of failure of dams depending upon salient characteristics of the event, quality of the rock constituting the foundation strata, material of the dam and the design criteria adopted. The design methodologies have undergone commendable changes from the linear-elastic static analyses to dynamic analyses and the design techniques are capable of incorporating non-linearity and also for simulating the near real scenario. The pseudo-static seismic methods gave way to dynamic seismic simulations using the time histories of the seismic activities already occurred with the help of various mathematical models and refined software. Concrete dams are no exception in failures, if they are not implemented and monitored as per the latest guidelines of national and international standards. Apart from seismicity, there are various factors influencing the behaviour and safety of dams. Concrete arch dams are often constructed to impound very large volume. Adoption of state of the art analyses techniques, design as per latest guidelines, studying the performance and behaviour, safety evaluation and continuous dam health monitoring are essential to avert any potential hazard to these invaluable resources. This paper reviews extensively, the various considerations towards the design, behaviour, performance and the failure scenarios of concrete arch dams.

Excessive sand mining to meet the growing demands of the construction industry has resulted in the degradation of rivers, lowering of groundwater table, saltwater intrusion into coastal aquifers, and damages to the biodiversity of the riverine ecosystem, besides endangering bridges and hydraulic structures at several locations. Methods presently being employed to assess the amount of sand that can be mined from rivers lack a scientific basis and are seldom supported by systematic studies on the behaviour of riverine systems. Sand audit reports shall be prepared based on hydrologic, hydraulic, and sediment transport modelling of rivers, and shall take into account relevant environmental and ecological considerations. These reports shall clearly present details pertaining to the annual sediment yield of the river basin, reaches of the river/ locations from which sand can be extracted without disturbing the river sediment equilibrium, and the volume of sediment that can be extracted from these locations. Sand mining from rivers is a major environmental issue in Kerala and the urgent need for regulating sand extraction based on a scientific assessment of the amount of sand available is widely recognized. It is in this context that this work aimed at developing a framework to perform sand auditing was taken up. The methodology is demonstrated by applying it to the Chaliyar River in Kerala. Rainfall-runoff and soil erosion modelling, and sediment routing were performed in HEC-HMS. Soil erosion from the catchment was modelled using the Modified Universal Soil Loss Equation (MUSLE) and the sediment was routed through the river by the uniform equilibrium method. Hydraulic and sediment transport modelling was then performed in HEC-RAS. Values of the model performance criteria for both HEC-RAS and HEC-HMS indicate that these models performed reasonably well. Based on the analysis, a sand audit report and sand volume map were prepared. [ABSTRACT FROM AUTHOR]

Heavy metals are discharged into the soil around us from various anthropogenic sources and also by the use of fertilizers, pesticides, pharmaceuticals, etc. In most cases, industrialization can be pointed to as the reason behind soil pollution. Contamination of soil leads to large-scale environmental degradation and health impacts. Many investigators have studied techniques for removing heavy metals from soil. Soil washing is an emerging area that can be implemented for this purpose. Studies were carried out in the controlled conditions of a laboratory environment to determine the suitability of soil-washing techniques for removing lead from polluted land. The results showing the influence of various parameters in soil washing, such as duration of washing, molar strength of the solution used, the weight ratio of soil to wash solution, etc., are presented in this paper. Batch studies were conducted to investigate the performance of chelating agents such as Na2EDTA, HCl, HNO3 and CaCl2 with regard to the removal of lead from artificially contaminated locally available soil. Based on the batch studies, it is observed that the strength of the washing solution, the proportion of soil and solution, the period of agitation, etc. influence the removal of contaminants. Based on the studies, it is concluded that, while recommending soil washing using chelating agents for remediating lead-contaminated soils, it is essential to identify the influencing parameters and determine the optimum conditions so that higher removal can be achieved without any adverse effect. [ABSTRACT FROM AUTHOR]